(1) Field of the Invention
The present invention relates in general to microwave circuits, and more particularly, to field-effect transistor circuits operating in the microwave frequency range.
(2) Description of the Prior Art
Field effect transistor circuits are generally conditionally stable at microwave frequencies. One method for stabilizing such circuits at UHF and below is to resistive load the device; however, this technique has not been effective at microwave frequencies.
In general a two port device, as schematically illustrated in FIG. 1, as may be defined in accordance with its S-parameters, as follows: ##EQU1## Such a two port device, for example, a transistor device, is potentially unstable at microwave frequencies, because the reverse transmission coefficient S.sub.12 is too large. Thus, if some means could be devised for reducing the reverse transmission coefficient sufficiently, the network can be made unconditionally stable.
Typical problems encountered in trying to reduce the reverse transmission coefficient of a two port device operating at microwave frequencies, such as the affect of additional conductive lead lines and the need to provide d.c. bias isolation between stages, has made stabilization of such devices difficult to accomplish in practice. Thus, the use of field effect transistors for microwave applications has been seriously restricted.